Injection molding method and apparatus therefor

ABSTRACT

An injection molding apparatus includes an injector that obtains molten resin by melting resin, and injects the molten resin, a hot runner that is a flowing path of the molten resin, and a temperature rising part that is provided in a part of the hot runner, and increases a temperature of the molten resin to be higher than a melting temperature in the injector.

TECHNICAL FIELD

The present invention relates to an injection molding method and aninjection molding apparatus, which obtain a molded product by fillingmolten resin in a cavity formed in a mold.

BACKGROUND ART

Injection molding is well known as a method of obtaining a moldedproduct by supplying molten resin injected from an injector to a cavityformed in a mold, and then curing the molten resin by cooling.

In injection molding, resin is melted in an injector, and obtainedmolten resin is injected from the injector and flowed in a hot runner.The molten resin is further led to a product part forming a part ofcavity, via a spool, a gate, and the like formed in a mold. Just before(an upstream side of) a cavity, a nozzle may be disposed as described inPatent Document 1, for example, and the molten resin may be led out froma nozzle and supplied to a cavity.

A temperature of a hot runner is kept at 200-220° C., for example, and atemperature of a mold is substantially at a room temperature. Therefore,the molten resin injected into a cavity is deformed (namely, molded)along the shape of the cavity, cured while decreasing a temperature byheat being removed, and formed as a molded product.

In such injection molding, it is attempted to decrease the amount ofresin to lower the product cost, or to produce a thin-wall product witha small thickness dimension (wall thickness) for the purpose ofobtaining a lightweight molded product to decrease CO2 emissions.However, in this case, if the injection conditions are the same as thosefor molding a thick-wall product, a flowing distance of molten resin maybe shorten.

When such a situation occurs, for example, molten resin does not reachan end of the product part. In other words, a filling defect occurs anda corresponding portion is lost, or so-called deformation occurs and adefective molded product is produced.

For avoiding such a problem, it is considered to increase a molten resininjection pressure. In this case, a pressing force to molten resin isincreased, and a flowing distance of molten resin is expected toincrease. However, when a molten resin injection pressure is increased,a burr is likely to occur on a parting surface, especially near a gate.Thus, it is also considerable to increase a mold clamping pressure tonarrow a gap causing a burr as much as possible. However, for obtaininga high mold clamping pressure, a large size or high power displacementmechanism is necessary for mold clamping/opening by displacing a movablemold. Thus, an injection molding apparatus is increased in size andweight. Further, such a displacement mechanism is generally expensive,and increases a capital investment.

From the above viewpoint, Patent Document 2 has proposed a method ofmolding a resin molded product having a thin-wall portion at a lowequipment cost. The method comprises forming first and second resinpaths in a mold, opening a valve provided in the second resin path aftermolten resin that is led to a product part from the first resin pathpasses through a portion forming a thin-wall portion, and supplying themolten resin from the second resin path to an unfilled portion of theproduct part.

In the related art described in the Patent Document 2, for storing avalve opening timing, or a timing of supplying molten resin from thesecond resin path, in a control unit, it is necessary to previouslydetermine a relationship between an elapsed time after start of moltenresin injection and a molten resin reaching position in a product partby repeating tests. This is troublesome, and takes a long time forperforming the tests.

As described in the paragraph [0027] of the Patent Document 2, it isalso considerable to provide a detection unit in a product part, and todetect that molten resin passes through a predetermined position byusing the detection unit. However, in this case, a molten resininjection pressure must be changed depending on the position of thedetection unit.

Thus, it is considered to increase a temperature of molten resin anddecrease a viscosity of molten resin by setting a high temperature formelting resin in an injector, and to lead the molten resin into a cavityafter maintaining the high temperature/low viscosity state in a hotrunner. However, in this case, according to the inventor's intensivestudies, a molded product with an insufficient strength may be oftenproduced due to a change in physical properties of the molten resin.

Moreover, the injection molding apparatus disclosed in the PatentDocument 2 is of a so-called multipoint gate type, in which a pluralityof gates is present for leading molten resign to a product part. Thus, aweld line is formed, degrading the external appearance quality of moldedproduct. In addition, a plurality of valve gates must be provided,increasing mold costs.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-A-11-105079

Patent Document 2: JP-A-2003-154562

SUMMARY OF INVENTION

Embodiments of the invention relate to an injection molding method andan injection molding apparatus, which can fill molten resin in an entireproduct part, avoid an increase in size and weight of an injectionmolding apparatus, avoid an increase of capital investment, obtain amolded product with a sufficient strength, reduce a cycle time to obtaina molded product, and avoid falling off of a molded product during moldopening.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus according to a first embodiment.

FIG. 2 is a schematic longitudinal sectional view of other parts of theinjection molding apparatus of FIG. 1.

FIG. 3 is a schematic side sectional view showing temperature variationsin fluid flowing in a straight tube.

FIG. 4 is a schematic side sectional view showing a fluid flowing statein a static mixer.

FIG. 5 is a schematic longitudinal sectional view of relevant partsshowing a state that molten resin remains in a temperature rising partafter injection molding.

FIG. 6 is a schematic longitudinal sectional view of relevant partsshowing a state that molten resin remained in a temperature rising partis pushed out from a temperature rising part by newly injected moltenresin.

FIG. 7 is a schematic longitudinal sectional view of relevant partsshowing a state that molten resin remained in a temperature rising partis further pushed out from the state of FIG. 6.

FIG. 8 is a schematic longitudinal sectional view of relevant partsshowing a state that molten resin remained in a temperature rising partis further pushed out from the state of FIG. 7, and stored in a slagwell.

FIG. 9 is a schematic longitudinal sectional view of relevant partsshowing a state that a part of remained molten resin stored in a slagwell is pushed out from a slag well, and led to a runner.

FIG. 10 is a schematic longitudinal sectional view of relevant partsshowing a state that a part of remained molten resin is further pushedout from the state of FIG. 9, and flows in a runner.

FIG. 11 is a schematic longitudinal sectional view of relevant partsshowing a state that a part of remained molten resin is further pushedout from the state of FIG. 10, and flows in a runner.

FIG. 12 is a schematic longitudinal sectional view of relevant partsshowing a state that a part of remained molten resin forms a skin layerand remains after being further pushed out from the state of FIG. 11,and flows in a runner.

FIG. 13 is a schematic longitudinal sectional view of relevant partsshowing a state that only newly injected molten resin is led to aproduct part.

FIG. 14 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus according to a second embodiment.

FIG. 15 is a schematic longitudinal sectional view of relevant partsshowing a state that a path opening/closing part shown in FIG. 14 opensan opening of an inlet side of a spool.

FIG. 16 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus in which a valve member constituting apath opening/closing part is provided without passing through a stirringpart.

FIG. 17 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus in which a valve member constituting apath opening/closing part is provided so as to be inclined to alongitudinal direction of a stirring part.

FIG. 18 is a magnified view of relevant parts showing a part near a tipof a valve member while the injection molding apparatus shown in FIG. 17is in an opened state.

FIG. 19 is a magnified view of relevant parts showing a part near a tipof a valve member while the injection molding apparatus shown in FIG. 17is in a closed state.

FIG. 20 is a magnified view of relevant parts showing an opened statewhen a shape of the tip of the valve member is different from those inFIG. 18 and FIG. 19.

FIG. 21 is a magnified view of relevant parts showing a closed statewhen a shape of the tip of the valve member is different from those inFIG. 18 and FIG. 19.

FIG. 22 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus in which a valve member is passedthorough avoiding a junction of stirring blades of a stirring part.

FIG. 23 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus having a configuration different fromthat shown in FIG. 9, in which a valve member is passed through avoidinga junction of stirring blades of a stirring part.

FIG. 24 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus in which a path opening/closing part isprovided in a movable mold.

FIG. 25 is a schematic longitudinal sectional view of relevant partsshowing a state that the path opening/closing part shown in FIG. 24opens an opening of an inlet side of a spool.

FIG. 26 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus having a configuration different fromthat shown in FIG. 24, in which a path opening/closing part is providedin a movable mold.

FIG. 27 is a schematic longitudinal sectional view of relevant partsshowing a state that the path opening/closing part shown in FIG. 26opens an opening of an inlet side of a spool.

FIG. 28 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus capable of opening/closing a downstreamside fluid path of a temperature rising part.

FIG. 29 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus provided with a plurality of temperaturerising parts and path opening/closing parts.

FIG. 30 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus in which a valve shaft (a valve member)is inserted into a tubular member, and passed through an insertion holeof a stirring part.

DESCRIPTION OF EMBODIMENTS

An injection molding apparatus and an injection molding method accordingto embodiments will be explained in detail with reference to theaccompanying drawings.

FIG. 1 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus 1010 according to a first embodiment. Theinjection molding apparatus 1010 comprises a fixed mold 1012, and amovable mold 1014 that moves close to or apart from the fixed mold 1012under the action of a not-shown displacement mechanism.

The fixed mold 1012 is additionally provided with a first hot runnerblock 1018 in which a first hot runner 1016 is formed. On the downstreamside of the first hot runner block 1018, a second hot runner block 1022in which a second hot runner 1020 is formed is provided.

A touch piece 1024 is provided in the first hot runner block 1018. Alead hole 1030 is formed as a through hole in the touch piece 1024. Aninjection nozzle 1034 of an injector 1032 is seated on an opening of thelead hole 1030.

The first hot runner 1016 communicates with the lead hole 1030. Thesecond hot runner 1020 comprises a communication path 1036 communicatingwith the first hot runner 1016, and a plurality of branch paths 1038branching radially from the communication path 1036. FIG. 1 shows twoout of the branch paths 1038 spaced 180° each other.

The branch path 1038 passes through a temperature rising part 1040 as anend portion of the second hot runner 1020, and communicates with aproduct part 1050 via a cobwebbing prevention part 1042, a spool 1044, arunner 1046, and a gate 1048 (refer to FIG. 2).

In the vicinity of the first hot runner 1016 and second hot runner 1020,a not-shown heating unit such as a heater is provided. Therefore, themolten resin flowing in the first hot runner 1016 and second hot runner1020 is kept at a predetermined temperature between 200° C. and 220° C.,for example.

The second hot runner 1020 is provided with a temperature rising part1040 so as to connect to the branch path 1038 via a hot nozzle 1052(refer to FIG. 1).

In the first embodiment, the temperature rising part 1040 is formed bywinding a first band heater 1056 around an outer circumferential wall ofa static mixer 1054. A small diameter end portion 1055 of the staticmixer 1054 is threaded. The threaded portion is engaged with a threadedportion provided in an end portion of the hot nozzle 1052.

The static mixer 1054 is, as well known, a tubular member provided witha mixing blade 1058 inside. The molten resin flowing in the static mixer1054 moves along a shape of the mixing blade 1058 when passing throughthe mixing blade 1058. While moving, the molten resin is stirred. Asseen from this fact, the static mixer 1054 is a stirring unit notrequiring power.

The first band heater 1056 wound around the outer circumferential wallof the static mixer 1054 transfers heat to the mixing blade 1058 throughthe outer circumferential wall. Therefore, the heat is transferred alsoto the molten resin passing through the mixing blade 1058, and ashearing heat is generated depending on a shape of the mixing blade1058. As a result, a temperature of the molten resin is increased. Inother words, the temperature rising part 1040 is configured to raise thetemperature of the molten resin flowing in the temperature rising part1040. A temperature of the temperature rising part 1040 is controlleddepending on a value measured through a first thermocouple 1060.

The cobwebbing prevention part 1042 continues to the temperature risingpart 1040. The cobwebbing prevention part 1042 comprises a tubularmember 1062, a second band heater 1064 wound around an outercircumference wall of the tubular member 1062, and a cobwebbingprevention ring 1066 housed inside the tubular member 1062.

In an end portion of the static mixer 1054, a threaded step part 1070 isformed in being recessed along the axial direction. On the other hand,the tubular member 1062 includes a small diameter part 1072 and a largediameter part 1074 in this order from the side close to the static mixer1054. The small diameter part 1072 closest to the static mixer 1054 isinserted into the threaded step part 1070. The small diameter part 1072has a threaded portion, which is engaged with the threaded portion ofthe threaded step part 1070.

A ring-shaped heat insulating member 1078 is externally fitted to theouter circumferential wall of the small diameter part 1072. By heatinsulating member 1078, the static mixer 1054 and tubular member 1062are thermally isolated. In other words, the heat of the static mixer1054 is prevented from transferring to the tubular member 1062.

The second band heater 1064 is wound around an outer circumferentialwall of the large diameter part 1074 of the tubular member 1062. Asecond thermocouple 1080 contacts the large diameter part 1074. Thefirst band heater 1056, second band heater 1064, first thermocouple1060, and second thermocouple 1080 are electrically connected to anot-shown control circuit. Therefore, the calorific values of the firstband heater 1056 and second band heater 1064 are adjusted under thecontrol action of the control circuit, depending on the temperatures ofthe temperature rising part 1040 and cobwebbing prevention part 1042detected by the first thermocouple 1060 and second thermocouple 1080. Asdescribed later, a temperature of the cobwebbing prevention part 1042 isset to be lower than that of the temperature rising part 1040.

In the tubular member 1062, a housing recessed portion 1082 is formed inthe large diameter part 1074. The cobwebbing prevention ring 1066 ishoused in the housing recessed portion 1082. The cobwebbing preventionring 1066 is widely used in injection molding of molten resin, and iswell known to those skilled in the art. Therefore, detailed explanationthereof is omitted.

The housing recessed portion 1082 houses also a nozzle tip 1084,provided with a spool 1044. The outer diameter of the nozzle tip 1084 issubstantially constant, but the diameter of the spool 1044 formed insidethe nozzle tip 1084 is gradually increased as if tapered from an endportion of the side (the upstream side) close to the tubular member 1062toward an end portion of the side (the downstream side) apart from thetubular member.

In the movable mold 1014, a slag well 1086 is formed extending along theaxial direction of the spool 1044. The total sum of the volume of theslag well 1086 and each of the spool 1044, the runner 1046, and the gate1048 is set greater than the volume of the static mixer 1054. Therefore,the entire molten resin remained in the static mixer 1054 forms a skinlayer in the spool 1044, slag well 1086, runner 1046, and gate 1048 atthe time of next injection molding.

The runner 1046 communicates with the slag well 1086. The axialdirection of the runner 1046 is substantially orthogonal to the axialdirection of the spool 1044. Thus, the flowing direction of the moltenresin led out from the spool 1044 is changed by the runner 1046.

In the downstream of the runner 1046, as shown in FIG. 2, agate 1048communicating with the runner 1046, and a product part 1050communicating with the runner 1046 through the gate 1048 are formed. Asdescribed above, the product part 1050 is positioned on a mating surfaceof the fixed mold 1012 and movable mold 1014.

In FIG. 1 and FIG. 2, the temperature rising part 1040, spool 1044, andrunner 1046 are magnified to facilitate understanding. The scales inFIG. 1 and FIG. 2 do not correspond to actual dimensions. For example,an axial dimension (length) of the static mixer 1054 is actually set tobe extremely smaller than those of the branch path 1038 and second hotrunner 1020. In other words, the flowing distance of molten resin in thestatic mixer 1054 is shorter than the flowing distances of molten resinin the branch path 1038 and second hot runner 1020.

The injection molding apparatus 1010 according to the first embodimentis basically configured as described above. Next, the functions andeffects of the injection molding apparatus 1010 will be explained inrelation to an injection molding method implemented in the injectionmolding apparatus 1010.

For injection molding, first, the movable mold 1014 is displaced towardthe fixed mold 1012 under the action of the not-shown displacementmechanism, and the mold is clamped. Before or after that, resin ismolten at a predetermined temperature in the injector 1032 to obtainmolten resin.

Next, the molten resin is injected from the injection nozzle 1034 of theinjector 1032. The injected molten resin reaches the first hot runner1016 through the lead hole 1030 formed in the touch piece 1024, and thenreaches the branch path 1038 through the communication path 1036 of thesecond hot runner 1020. The molten resin flows further along each of thebranch paths 1038.

As described above, the first hot runner 1016 and second hot runner 1020are heated by a not-shown heating unit (a heater or the like). Thus, themolten resin flows in the first hot runner 1016 and second hot runner1020 in being kept substantially at a melting temperature. Of course,this temperature can ensure a sufficient strength when the molten resinis cured by cooling to become a molded product.

A melting temperature or a holding temperature is set in accordance withtypes of molten resin, generally between 200° C.-220° C., morepreferably between 205° C.-215° C.

The molten resin flowing in the branch path 1038 of the second hotrunner 1020 is led out from the hot nozzle 1052 to the inside of thestatic mixer 1054 constituting the temperature rising part 1040. Heatfrom the first band heater 1056 is transferred to the static mixer 1054so that the inside of the static mixer 1054 is heated to be higher thana melting temperature in the injector 1032. Therefore, the heat is alsotransferred to the molten resin passing through the mixing blade 1058.As a result, the molten resin is heated to be higher than the meltingtemperature in the injector 1032 or the temperature while flowing in thebranch path 1038, and the viscosity is lowered accordingly.

A setting temperature of the static mixer 1054 is preferably 10° C.-150°C., more preferably 20° C.-100° C. higher than the melting temperaturein the injector 1032. Such temperatures can avoid production of a moldedproduct with an insufficient strength.

The molten resin is heated by receiving a shearing force while passingthrough the mixing blade 1058. In other words, the molten resintemperature is increased only by passing through the mixing blade 1058.If the temperature increase is sufficient, the static mixer 1054 may beset to the same temperature as the melting temperature in the injector1032.

The power consumption of the injection molding apparatus 1010 can besuppressed by setting the melting temperature in the injector 1032 to aminimum value required to melt the resin, and setting the temperature ofthe temperature rising part 1040 to a minimum value required to obtainthe viscosity of molten resin required to fill in the entire productpart 1050.

In a case where a simple straight tube 1090 is disposed in thetemperature rising part 1040 (refer to FIG. 3), actually, temperaturevariations occur inside the straight tube 1090. In other words, atemperature is high in a part close to the inner circumferential wall,and is low in a part close to the diameter center. Thus, temperaturevariations occur also in the molten resin flowing in the straight tube1090, and it may not be easy to obtain the same viscosity of moltenresin in any part in the straight tube 1090.

Contrarily, in the embodiment provided with the static mixer 1054, asshown in FIG. 4, along with passing the molten resin through the mixingblade 1058, the molten resin close to the inner circumference wall movestoward the diameter center, and the molten resin close to the diametercenter moves toward the inner circumferential wall. Thus, the moltenresin moved close to the first band heater 1056 as a heat source andheated to a relatively high temperature and the molten resin moved awayfrom the first band heater 1056 and kept at a relatively low temperatureare continuously mixed and flowed in the static mixer 1054. Therefore,occurrence of temperature variations in molten resin can be avoided. Asa result, it is possible to obtain the molten resin with substantiallythe same temperature, or with substantially the uniform viscosity, inany part.

Moreover, even if a starting material is a master batch material ormetallic dyed material, such a material is sufficiently dispersed bystirring of the static mixer 1054, and it is possible to obtain a moldedproduct with excellent external appearance quality. Further, after firsttime injection molding, when second time injection molding is performedby changing the color and type of the starting material, even if themolten resin injected in the first time injection molding remains andmixes with newly injected molten resin, both molten resins aresufficiently stirred by the static mixer 1054, and a defectiveappearance such as a stripe, for example, caused by the remained moltenresin is difficult to occur in a molded product. This can decrease thenumber of defective products.

In addition, use of the static mixer 1054 does not require power forstirring. This avoids a complex configuration of the injection moldingapparatus 1010. At the same time, an increase of mold investment can beavoided, and power consumption is not increased.

The molten resin passed through the temperature rising part 1040 is ledto the cobwebbing prevention part 1042. The cobwebbing prevention part1042 is set to a temperature of 50° C.-100° C., typically about 80° C.lower than the temperature rising part 1040. However, the length of thetubular member 1062 is extremely shorter than the length of the staticmixer 1054, and the mixing blade 1058 is not present in the tubularmember 1062. Thus, the molten resin flowing in the cobwebbing preventionpart 1042 is led out from the cobwebbing prevention ring 1066 to thespool 1044 without substantially decreasing the temperature.

After passing through the spool 1044, the molten resin is led to theproduct part 1050 via the runner 1046 and gate 1048 (refer to FIG. 2).As described above, the viscosity of molten resin is lowered by that themolten resin temperature is increased in the temperature rising part1040. Therefore, the flowing distance is increased, and even if there isa portion forming a thin wall portion in the product part 1050, themolten resin easily passes through the portion, and reaches an endportion of the product part 1050.

The product part 1050 is usually adjusted to substantially a roomtemperature. Therefore, the molten resin led to the product part 1050 iscooled and cured by that the heat is removed. Thereby, a molded productcan be obtained.

Before being led to the temperature rising part 1040, the molten resinis kept at a temperature capable of ensuring a sufficient strength whenit is cooled and cured to become a molded product, and is flowed in thesecond hot runner 1020, communication path 1036, and branch path 1038.Thereafter, the molten resin passes through the temperature rising part1040, but the flowing time is short. In other words, the time while themolten resin temperature is higher than the melting temperature in theinjector is short. Thus, a change in physical properties of the moltenresin can be avoided, and a molded product with a sufficient strengthcan be obtained. Moreover, as the molten resin has reached to the endportion of the product part 1050 and cured by cooling, occurrence ofdefects in the molded product can be avoided.

Further, it is unnecessary to increase a molten resin injectionpressure, and it is unnecessary to increase a mold clamping pressure toavoid occurrence of burrs. Therefore, a displacement mechanism (ahydraulic cylinder or the like) for clamping and opening a mold may becompact. This avoids an increase in the size and weight of the injectionmolding apparatus 1010. Further, as an expensive displacement mechanismis unnecessary, an increase of capital investment can be avoided.

Moreover, in the embodiment, a multipoint gate is not used, and it isunnecessary to worry about occurrence of a weld line. In addition, it isonly necessary to control a temperature of the temperature rising part1040, and it is unnecessary to repeat a test for setting injectionconditions.

By opening a mold by separating the movable mold 1014 from the fixedmold 1012 under the action of the displacement mechanism, a moldedproduct can be exposed. A molded product is pushed out by a knockout pin(not shown), for example, and separated from the injection moldingapparatus 1010.

A molded product is obtained as a piece that the resin remained andcured by cooling in the spool 1044, runner 1046, and gate 1048 isintegrally connected to a product part. Such a portion is cut off from aproduct part of a molded product, and crushed for use as a startingmaterial in the next injection molding.

In the embodiment, the cobwebbing prevention part 1042 is provided. Whenmolten resin remains in the cobwebbing prevention part 1042 for a longtime, the molten resin temperature is decreased to be lower than thetemperature while passing through the temperature rising part 1040.Because, the cobwebbing prevention part 1042 has been set to atemperature lower than the temperature rising part 1040. Further, thefact that transfer of the heat of the static mixer 1054 to the tubularmember 1062 is suppressed by the heat insulating material 1078contributes to keep the temperature of the cobwebbing prevention part1042 lower than the temperature rising part 1040.

The molten resin decreased in temperature is sufficiently lowered inviscosity. Further, the cobwebbing prevention part 1042 is provided withthe cobwebbing prevention ring 1066. These are combined to preventoccurrence of cobwebbing during mold opening.

After performing the above injection molding, as shown in FIG. 5, themolten resin may remain in the temperature rising part 1040. Theremained molten resin is, as shown in FIG. 6, pushed out to the spool1044 by newly injected molted resin that passes through the second hotrunner 1020 and branch path 1037, and reaches the temperature risingpart 1040 in the next injection molding. To clearly discriminate betweenthe remained molten resin and the newly injected molten resin, theformer is designated by a reference numeral 1100, the latter isdesignated by a reference numeral 1102, and they are marked by differenthatching.

The remained molten resin 1100 is partially adhered to the innercircumferential wall of the spool 1044 by a fountain flow describedlater. On the other hand, the other is pushed out toward the runner 1046as shown in FIG. 7, and is stored in the slag well 1086 and runner 1046as a result, as shown in FIG. 8. In other words, the slag well 1086receives the pushed-out remained molten resin 1100.

The newly injected molten resin 1102 flows further while pressing a partnear the center of the remained molten resin 1100, as shown in FIG. 9 toFIG. 12. In other words, a flow (a fountain flow) from the center to thewall surface of the runner 1046 occurs in the remained molten resin1100.

The remained molten resin 1100 is pressed to the wall surface of therunner 1046 by the fountain flow, and the heat of the molten resin isremoved by the wall surface. Thus, the remained molten resin 1100 nearthe wall surface is cooled and cured, and is adhered to the wall surfaceas a skin layer. As the total sum of the volume of the slag well 1086,the spool 1044, the runner 1046, and the gate 1048 is set higher thanthe volume of the static mixer 1054, formation of a skin layer iscompleted in the gate 1048 even at a maximum. FIG. 12 shows the casewhere adhesion of the remained molten resin 1100 to the wall surface iscompleted in the upstream side of the gate 1048. Thus, as seen from FIG.13, the remained molten resin 1100 is prevented from being led to theproduct part 1050 in the next injection molding.

The remained molten resin 1100 has been stored in the high-temperaturetemperature rising part 1040 before the next injection molding isstarted after the last injection molding is finished. Thus, when theremained molten resin 1100 is led to the product part 1050, there is apossibility of producing a molded product with an insufficient strength.However, in the embodiment, the remained molten resin 1100 istemporarily received by the slag well 1086, and when the new moltenresin 1102 flows, a fountain flow is generated to adhere the moltenresin to the wall surfaces of the spool 1044 and runner 1046 as a skinlayer. Thus, the remained molten resin 1100 is prevented from being ledto the product part 1050. This eliminates the possibility of producing amolded product with an insufficient strength.

The skin layer is integrated with a cured product produced when the newmolten resin 1102 remained in the runner 1046 is cooled and cured. Asdescribe above, after the mold is opened, the cured product is cut offfrom the product part of the molded product.

FIG. 14 is a schematic longitudinal sectional view of relevant parts ofan injection molding apparatus 10 according to a second embodiment. Theinjection molding apparatus 10 comprises a fixed mold 12, and a movablemold 14 that moves close to or apart from the fixed mold 12 under theaction of a not-shown displacement mechanism. The fixed mold 12 andmovable mold 14 form a cavity including a runner 16.

The fixed mold 12 is additionally provided with a hot runner block 20 inwhich a first hot runner 1016 is formed. On the downstream side of thehot runner block 20, a second hot runner manifold 24 in which a secondhot runner 22 is formed is provided.

A touch piece 26 is provided in the hot runner block 20. A lead hole 28is formed passing through the touch piece 26. An injection nozzle 32 ofan injector 30 is seated on an opening of the lead hole 28.

The first hot runner 18 communicates with the lead hole 28. The secondhot runner 22 comprises a guide path 34 communicating with the first hotrunner 18, and a plurality of branch paths 36 branching radially fromthe guide path 34. FIG. 14 shows two out of the branch paths 36 spaced180° each other.

The second hot runner 22 further comprises a communication path 40provided in the hot nozzle 38, and a temperature rising part 42 as anend portion. Namely, the branch path 36 communicates with thetemperature rising part 42 through the communication path 40. In otherwords, the communication path 40 is an upstream side flowing path of thetemperature rising part 42.

In the vicinity of the first hot runner 18, the branch path 36, and thecommunication path 40, a not-shown heating unit such as a heater isprovided. Therefore, molten resin flowing in the first hot runner 18,the branch path 36, and the communication path 40 is kept at apredetermined temperature between 200° C. and 220° C., for example.

In the second embodiment, the temperature rising part 42 is configuredby winding a band heater 46 around an outer circumferential wall of astatic mixer 44. An inside wall of an end portion of the static mixer 44facing the hot nozzle 38 is threaded. The threaded portion is engagedwith a threaded portion provided on an outside wall of an end portion ofthe hot nozzle 38 facing the static mixer 44.

The static mixer 44 is, as well known, a tubular member provided with amixing blade 48 inside. Molten resin flowing in the static mixer 44moves along a shape of the mixing blade 48 when passing through themixing blade 48. While moving, the molten resin is stirred. As seen fromthis fact, the static mixer 44 is a stirring unit not requiring power.

The band heater 46 wound around the outer circumferential wall of thestatic mixer 44 transfers heat to the mixing blade 48 through the outercircumferential wall. Therefore, the heat is transferred also to themolten resin flowing in the mixing blade 48. Shearing heat is generateddepending on a shape of the mixing blade 48. Therefore, a temperature ofthe molten resin is increased. In other words, the temperature risingpart 42 is configured to raise the temperature of the molten resinflowing in the heat rising part 42. A temperature of the band heater 46,consequently, a temperature of the temperature rising part 42 iscontrolled depending on a value measured through a not-shownthermocouple.

In the downstream side of the static mixer 44, a nozzle tip 52 providedwith a spool 50 is disposed. Molten resin passing through thetemperature rising part 42 is led to the runner 16 as a part of a cavityvia the spool 50. In other words, the spool 50 is a downstream sideflowing path of the temperature rising part 42. The diameter of thespool 50 is gradually increased as if tapered from an end portion of theside (the upstream side) close to the temperature rising part 42 towardan end portion of the side (the downstream side) close to the movablemold 14.

In the above configuration, the hot runner block 20 or the hot runnermanifold 24 is provided with a hydraulic cylinder (a displacementmechanism) that constitutes a path opening/closing part. In other words,the hydraulic cylinder 54 is supported by the fixed mold 12 via the hotrunner block 20 or the hot runner manifold 24. Otherwise, the hydrauliccylinder 54 may be directly provided in the fixed mold 12.

A valve shaft 60 (a valve member) that constitutes the pathopening/closing part together with the hydraulic cylinder 54 isconnected to a front end of a piston rod 56 of the hydraulic cylinder 54via a coupling 58. The valve shaft 60 is supported by a bearing 62provided in the hot runner manifold 24, and is inserted into the branchpath 36. The valve shaft 60 extends beyond a communication path 40 ofthe hot nozzle 38 and the temperature rising part 42.

On the other hand, the mixing blade 48 is provided with a plurality ofinsertion holes along a central axis of the static mixer 44. The valveshaft 60 is inserted into all insertion holes, and is entered into theinside of the nozzle tip 52.

In the spool 50, the size of the opening on the side facing thetemperature rising part 42 is substantially equal to the size of thefront end portion of the valve shaft 60. Thus, the front end of thevalve shaft 60 can close the opening. Of course, when the valve shaft 60is retreated rightward in FIG. 14, the opening is opened (refer to FIG.15). In other words, the inside wall near the opening functions as avalve seat.

The movable mold 14 is provided with the runner 16 constituting a partof the cavity and a not-shown gate. A product part to obtain a moldedproduct is provided in the downstream of the gate. In other words, thespool 50 communicates with the product part via the runner 16 and thegate.

The axial direction of the runner 16 is substantially orthogonal to theaxial direction of the spool 50. Thus, the flowing direction of themolten resin led out from the spool 50 is changed by the runner 16.

In FIG. 14 and FIG. 15, the temperature rising part 42, spool 50, andrunner 16 are magnified to facilitate understanding. The scales in FIG.14 and FIG. 15 do not correspond to actual dimensions. For example, theaxial dimension (length) of the static mixer 44 is actually set to beextremely smaller than that of the first hot runner 18 and branch path36. Of course, this is the same for the length dimension of the valveshaft 60. In other words, the flowing distance of molten resin in thestatic mixer 44 is shorter than the flowing distances of molten resin inthe first hot runner 18 and branch path 36. Therefore, the amount ofmolten resin remained inside the temperature rising part 42 is small.

The injection molding apparatus 10 according to the embodiment isbasically configured as described above. Next, the function and effectwill be explained in relation to an injection molding method implementedin the injection molding apparatus 10.

For injection molding, first, the movable mold 14 is displaced towardthe fixed mold 12 under the action of the not-shown displacementmechanism, and the molds are clamped. Before or after that, resin ismolten at a predetermined temperature in the injector 30 to obtainmolten resin.

Next, by biasing the hydraulic cylinder 54 and retreating the piston rod56, the valve member is moved back rightward, and the valve shaft 60 isseparated from the inside wall (valve seat) near the opening as shown inFIG. 15. Then, the spool 50 is released, and the lead hole 28communicates with the cavity via the first hot runner 18, second hotrunner 22 (guide path 34, branch path 36, and temperature rising part42), spool 50, and runner 16.

After communicating from the lead hole 28 to the cavity as describedabove, the molten resin is injected from the injection nozzle 32 of theinjector 30. The injected molten resin reaches the first hot runner 18through the lead hole 28 formed in the touch piece 26, and then reachesthe branch path 36 through the guide path 34 of the second hot runner22. The molten resin flows further along each of the branch paths 36.

As described above, the first hot runner 18 and second hot runner 22 areheated by a not-shown heating unit (a heater or the like). Thus, themolten resin flows in the first hot runner 18 and second hot runner 22in being substantially kept at a melting temperature. Of course, thistemperature can ensure a sufficient strength when the molten resin iscured by cooling to become a molded product.

A melting temperature or a holding temperature is set in accordance witha type of molten resin, generally between 200° C.-220° C., morepreferably between 205° C.-215° C.

The molten resin flowing in the branch path 36 of the second hot runner22 is led from the communication path 40 of the hot nozzle 38 to theinside of the static mixer 44 constituting the temperature rising part42. Heat from the band heater 46 is transferred to the static mixer 44so that the inside of the static mixer 44 is heated to be higher than amelting temperature in the injector 30. Further, when the molten resinpasses through the mixing blade 48, shearing heat is generated. The heatis transferred to the molten resin passing through the mixing blade 48.As a result, the molten resin is heated to be higher than the meltingtemperature in the injector 30 or the temperature while flowing in thebranch path 36, and the viscosity is lowered accordingly.

A setting temperature of the static mixer 44 is preferably 10° C.-150°C., more preferably 20° C.-100° C. higher than the melting temperaturein the injector 30. Such temperatures can avoid production of a moldedproduct with an insufficient strength.

The molten resin is heated by receiving a shearing force when passingthrough the mixing blade 48. In other words, the molten resintemperature is increased only by passing through the mixing blade 48. Ifthe temperature increase is sufficient, the static mixer 44 may be setto the same temperature as the melting temperature in the injector 30.

The power consumption of the injection molding apparatus 10 can bereduced by setting the melting temperature in the injector 30 to aminimum value required to melt the resin, and setting the temperature ofthe temperature rising part 42 to a minimum value required to obtain theviscosity of molten resin required to fill in the entire product part.

In the embodiment provided with the static mixer 44, along with passingthe molten resin through the mixing blade 48, the molten resin close tothe inner circumference wall moves toward the diameter center, and themolten resin close to the diameter center moves toward the innercircumferential wall. Thus, the molten resin moved close to the bandheater 46 as a heat source and heated to a relatively high temperatureand the molten resin moved away from the band heater 46 and kept at arelatively low temperature are continuously mixed and flowed in thestatic mixer 44. Therefore, occurrence of temperature variations in themolten resin can be avoided. As a result, it is possible to obtain themolten resin with substantially the same temperature, or withsubstantially the uniform viscosity, in any part.

Moreover, even if a material for obtaining molten resin is a masterbatch material or metallic dyed material, it is sufficiently dispersedby stirring of the static mixer 44, and a molded product with excellentexternal appearance quality can be obtained. Further, after the firsttime injection molding, when second time injection molding is performedby changing a color and type, even if the molten resin injected in thefirst time injection molding remains and mixes with newly injectedmolten resin, both molten resins are sufficiently stirred by the staticmixer 44, and an appearance defect like a stripe, for example, caused bythe remained molten resin is difficult to occur in a molded product.Thus, the number of defective products can be decreased.

In addition, use of the static mixer 1054 does not require power forstirring. This avoids a complex configuration of the injection moldingapparatus 10. At the same time, an increase of mold investment can beavoided, and power consumption is not increased.

The molten resin passed through the temperature rising part 42 passesthrough the spool 50, and is led to the product part via the runner 16and a not-shown gate. As described above, the temperature of the moltenresin led to the runner 16 is increased by the temperature rising part42, and the viscosity is sufficiently lowered. Further, as the moltenresin temperature is increased to be relatively high by the temperaturerising, even if the heat of the molten resin is removed by the movablemold 14, the temperature is hard to decrease. Therefore, the moltenresin flowing distance is increased, and even if there is a portionforming a thin wall portion in the product part, the molten resin easilypasses through the portion, and reaches an end portion of the productpart. In other words, the molten resin is densely filled in the entirecavity.

When a predetermined time elapses after the molten resin is injected,the hydraulic cylinder 54 is biased, and the piston rod 56 is movedforward to the right. Following the movement, the valve shaft 60 is alsomoved forward to the right, and the front end is attached to the insidewall (valve seat) near the opening. In other words, the spool 50 isclosed.

The product part is usually adjusted to substantially a roomtemperature. Therefore, the heat of the molten resin led to the productpart is removed. Further, as the spool 50 is closed, the molten resinfilled in the cavity is isolated from the molten resin in thetemperature rising part 42. Thus, the heat of the molten resin in thetemperature rising part 42 is prevented from transferring to the moltenresin filled in the cavity.

For the above reasons, the molten resin filled in the cavity isefficiently cooled and cured to become a molded product. In other words,according to the embodiment, it is possible to reduce the cycle timefrom starting injection of molten resin to obtaining a molded product.

Before being led to the temperature rising part 42, the molten resin iskept at a temperature capable of ensuring a sufficient strength whencooled and cured to become a molded product, and is flowed in the firsthot runner 18, guide path 34, and branch path 36. Thereafter, the moltenresin passes through the temperature rising part 42, but the flowingtime is short. In other words, the time while the molten resintemperature is higher than the melting temperature in the injector isshort. Thus, a change in physical properties of the molten resin can beavoided, and a molded product with a sufficient strength can beobtained. Moreover, as the molten resin has reached to the end portionof the product part and cured by cooling, occurrence of defects in themolded product can be avoided.

Further, it is unnecessary to increase a molten resin injectionpressure, and it is unnecessary to increase a mold clamping pressure toavoid burrs. Therefore, a displacement mechanism (a hydraulic cylinderor the like) for clamping and opening a mold may be compact. This avoidsan increase in the size and weight of the injection molding apparatus10. Further, as an expensive displacement mechanism is unnecessary, anincrease of capital investment can be avoided.

Moreover, in the embodiment, a multipoint gate is not used, and it isunnecessary to worry about occurrence of a weld line. In addition, it isonly necessary to control a temperature of the temperature rising part42, and it is unnecessary to repeat a test for setting injectionconditions.

By opening a mold by separating the movable mold 14 from the fixed mold12 under the action of the displacement mechanism, a molded product canbe exposed. A molded product is pushed out by a knockout pin (notshown), for example, and separated from the injection molding apparatus10.

A molded product is obtained as a piece that the resin remained andcured by cooling in the spool 50, runner 16, and gate is integrallyconnected to a product part. Such a portion is cut off from a productpart of a molded product, and crushed for use as a starting material inthe next injection molding.

The molten resin remained in the temperature rising part 42 is kept warmby the hand heater 46. Further, the remained molten resin is isolatedfrom the molten resin filled in the cavity, and is prevented from heatloss by the molten resin filled in the cavity. Therefore, the moltenresin remained in the temperature rising part 42 is maintained in amolten state, and is filled in the cavity in the same way when the nextinjection molding is performed.

Therefore, in the next injection molding, it is avoided that a curedpiece of the molten resin remained in the temperature rising part 42 ismixed in a molded product as a foreign matter. Thus, a molded productwith excellent appearance without defects can be obtained. Of course,occurrence of burrs can also be prevented as described above. In otherwords, the quality of a molded product is not affected byopening/closing of the spool 50 by the valve shaft 60.

As well known, the mixing blade 48 is formed by combined a plurality ofstirring blades 70 by brazing. Each blade is combined at the center ofradial direction. In other words, in the above embodiment, an insertionhole for passing the valve shaft 60 is formed in the joint part. In sucha case, when a molten resin injection pressure is extremely high, themixing blade 48 may be deformed.

When there is such a possibility, for example, a bypass block 72 isprovided between the temperature rising part 42 and the nozzle tip 52,as shown in FIG. 16. The bypass block 72 may be supported by the fixedmold 12 via a positioning pin 74. In FIG. 16, reference numerals 76, 78and 80 denote a positioning ring, a position pin, and a support block,respectively. In this case, a bearing 62 is provided in the bypass block72.

In the bypass block 72, a passageway 82 is formed as a communicationpath. A longitudinal direction of the passageway 82 obliquely crosses alongitudinal direction of the static mixer 44 at a predetermined angle.On the other hand, the valve shaft 60 extends parallel to thelongitudinal direction of the static mixer 44. In other words, the valveshaft 60 and static mixer 44 are placed in parallel to each other.

In this case, although the temperature rising part 42 is separated fromthe spool 50, as the passageway 82 is formed between them, thetemperature rising part 42 communicates with the spool 50 via thepassageway 82. Thus, the molten resin can be filled in the cavity in thesame way as described above.

Otherwise, as shown in FIG. 17, the valve shaft 60 may be extended in adirection inclined to the longitudinal direction of the static mixer 44.In this case, the bearing 2 can be provided on the outside wall of thestatic mixer 44, for example. In this case, as shown in FIG. 18 and FIG.19, the inside wall of the opening of the inlet side of the spool 50 maybe shaped to permit to seat on and separate from a front end of theobliquely extending valve shaft 60.

FIG. 18 and FIG. 19 show the case where the front end of the valve shaft60 is substantially hemispherical. However, as shown in FIG. 20 and FIG.21, even when the front end is conic trapezoidal, the shape of theinside wall of the opening of the inlet side of the spool 50 may bematched to the shape of the front end of the valve shaft 60.

Further, as shown in FIG. 22, the insertion hole may be formed so as toavoid a junction of the stirring blades 70 (the center in the radialdirection). In this case, the communication path 40 of the hot nozzle 38may be inclined like a crank or a reducer, so that the axial center(diameter center) of the outlet of the communication path 40 aligns withaxial center (diameter center) of the static mixer 44, and the axialcenter of the spool 50 may be provided at a position offset from theaxial center of the static mixer 44. Otherwise, as shown in FIG. 23, thecommunication path 40 of the hot nozzle 38 may be provided at a positionoffset from the axial center of the hot nozzle 38.

By aligning the axial center of the outlet of the communication path 40with the axial center of the temperature rising part 42 as descriedabove, the molten resin is prevented from staying between thecommunication path 40 and the temperature rising part 42.

The above embodiment explains with an example of providing a pathopening/closing part in the fixed mold 12. A path opening/closing partmay be provided in the movable mold 14.

For example, in the embodiment shown in FIG. 24, the movable mold 14 isprovided with a displacement mechanism comprising a motor 90, a rotationaxis 92, a pinion gear 94, and a rack 96. A bearing 98 is interposedbetween the rotation axis 92 and the movable mold 14.

The valve shaft 60 is connected to the front end of the rack 96 via acoupling 58. The front end of the valve shaft 60 is attached to ordetached from the inside wall near the opening of the inlet side of thespool 50. In other words, when injection molding is performed, the motor90 is biased, and thereby the rotation axis 92 starts rotation.Following this, when the pinion gear 94 provided in the rotation axis 92rotates, the rack 96 engaged with the pinion gear 94 moves backward. Asa result, as shown in FIG. 25, the valve shaft 60 is displaced leftward,and its front end is separated from the inside wall of the opening ofthe inlet side of the spool 50. Therefore, as described above, the partfrom the lead hole 28 to the cavity is continued.

In this state, molten resin is supplied. The molten resin passes throughthe temperature rising part 42, and is filled in a product part via therunner 16. When the filling is completed, the motor 90 is biased again,and the rack 96 is moved forward. Following this, the valve shaft 60 isdisplaced rightward, and its front end closes the opening of the inletside of the spool 50 as in FIG. 24. Thereafter, the molten resin iscooled and cured, and a molded product can be obtained in a state thatthe valve shaft 60 has entered.

After obtaining a molded product in such a manner, a mold is opened. Atthis time, the molded product is supported by the retreated valve shaft60. This eliminates a possibility that the molded product drops off froma mold. At this time, the molded product is being fixed to the movablemold 14.

After the mold is opened, a not-shown ejector pin works, pushes out themolded product, and separates it from the movable mold 14. The motor 90is biased again if necessary, and the valve shaft 60 is displacedrightward. In other words, the molded product is kept in being supportedby the valve shaft 60, and prevented from falling off.

After the molded product is removed from the valve shaft 60, the ejectorpin and the valve shaft 60 are displaced leftward, and returned to theoriginal positions. In the molded product, a portion where the valveshaft 60 has passed through becomes a through-hole, but this portion maybe cut off including a surrounding part, and may be reused.

When there is no possibility of falling off the molded product, themolded product may be separated from the movable mold 14 by operatingonly the ejector pin without displacing the valve shaft 60 rightward. Atthis time, the valve shaft 60 may be returned to the original positionby displacing leftward.

As shown in FIG. 26, the displacement mechanism may be configured toinclude a first cam member 104 and a second cam member 106 provided in apiston rod 102 of a hydraulic cylinder 100. In other words, the firstcam member 104 is provided with a convex cam portion 108 extending in adirection inclined to the longitudinal direction of the piston rod 102,and the second cam member 106 is provided with a concave cam portion 110engaging with the convex cam portion 108. Of course, the convex camportion 108 slidably engages with the concave cam portion 110.

In this case, the valve shaft 60 is connected to the second cam member106 via the coupling 58 provided at the front end of the second cammember 106. The front end of the valve shaft 60 is, as described above,attached to or detached from the inside wall near the opening of theinlet side of the spool 50. In other words, when injection molding isperformed, the hydraulic cylinder 100 is biased, and thereby the pistonrod 102 is moved down. At this time, as the convex cam portion 108 isbeing slidably engaged with the concave cam portion 110, the second cammember 106 is displaced leftward. As a result, as shown in FIG. 27, thevalve shaft 60 is displaced leftward, and its front end is separatedfrom the inside wall near the opening of the inlet side of the spool 50.Therefore, as described above, the part from the lead hole 28 to thecavity is continued.

In this state, molten resin is supplied. The molten resin passes throughthe temperature rising part 42, and is filled in a product part throughthe runner 16. When the filling is completed, the hydraulic cylinder 100is biased again. Thereby, the piston rod 102 is moved upward, and thesecond cam member 106 is displaced rightward under the actions of theconvex cam portion 108 and the concave cam portion 110. Following this,the valve shaft 60 is displaced rightward, and its front end closes theopening of the inlet side of the spool 50 as in FIG. 26. Thereafter, themolten resin is cooled and cured, and a molded product can be obtainedin a state that the valve shaft 60 has entered.

Thereafter, the same operations as those in the embodiment shown in FIG.24 and FIG. 25 are performed. Namely, after the mold is opened, themolded product is pushed out and separated from the movable mold 14under the action of the ejector pin. At this time, the hydrauliccylinder 100 is biased again if necessary, and the valve shaft 60 isdisplaced rightward. Of course, when there is no possibility of fallingoff the molded product, the molded product may be separated from themovable mold 14 by operating only the ejector pin without displacing thevalve shaft 60 rightward. At this time, the valve shaft 60 may bereturned to the original position by displacing leftward.

After the molded product is removed from the valve shaft 60, the ejectorpin and the valve shaft 60 are displaced leftward, and returned to theoriginal positions. A portion that the valve shaft 60 has passed throughbecomes a bottomed hole or a through-hole, but this portion may be cutoff including a surrounding part.

Apart from the above, as shown in FIG. 28, the communication path 40that is a downstream side flowing path of the temperature rising part 42may be opened or closed. In this case, the inlet opening (upstream side)facing the branch path 36 of the communication path 40 of the hot nozzle38 is narrowed like a reducer. The valve shaft 60 is attached to ordetached from the inside wall near the narrowed opening.

Further, as shown in FIG. 29, it is permitted to provide more than onetemperature rising part 42 and path opening/closing part. In this case,for example, when the runner 16 and product part are gradually expandedtoward the product part located below, a sequence may be controlled soas to sequentially bias the hydraulic cylinders 54 from the highestpositioned one downward.

In other words, in this case, the uppermost hydraulic cylinder 54 isbiased, the valve shaft 60 opens the opening of the inlet side of thespool 50, and thereby the molten resin of only the uppermost spool 50 isled to the runner 16. Then, the middle hydraulic cylinder 54 is biased,the valve shaft 60 opens the opening of the inlet side of the spool 50,and thereby the molten resin of the uppermost and middle spools 50 isled to the runner 16.

Finally, the lowermost hydraulic cylinder 54 is biased, and the valveshaft 60 opens the opening of the inlet side of the spool 50. Thereby,the molten resin of all the uppermost, middle, and lowermost spools 50is led to the runner 16.

As described above, by providing more than one temperature rising part42 and path opening/closing part so that they replenish the fillingamount to one another, even if the runner 16 and product part are wide,the molten resin can be supplied to the cavity without exclusivelyincreasing the injection pressure and mold clamping force, and a moldedproduct can have excellent external appearance quality without a weld.

The present invention is not to be limited to the embodiments describedabove, and may be modified in various ways without departing from itsspirit and essential characteristics.

For example, in the embodiments, the temperature rising part 1040 or 42is formed by winding the band heater 1056 or 46 around the static mixer1054 or 44. The temperature rising part 1040 or 42 may be formed byburying a coil heater or a cartridge heater in the static mixer 1054 or44.

Further, a stirring part is not to be limited to the static mixer 1054or 44. For example, it may be a screw that is rotated by power.

A stirring part is not indispensable. It may be omitted when a straighttube with a small diameter and small temperature variations is used forthe temperature rising parts 1040 or 42, for example.

Further, it is needless to say that an air cylinder can be used insteadof the hydraulic cylinder 54 or 100.

Further, when the remained molten resin 1100 in the temperature risingpart 1040 can be formed as a skin layer in the spool 1044, runner 1046,and gate 1048, it is unnecessary to provide the slag well 1086.

In the cobwebbing prevention part 1042, a member for accelerating heatradiation may be provided by externally fitting a radiation ring to thetubular member 1062.

Further, as shown in FIG. 30, a pipe 120 (a tubular member) may bepassed through the insertion hole formed in the mixing blade 48. In thiscase, the valve shaft 60 may be passed through a through-hole of thepipe 120. In other words, the valve shaft 60 is passed through theinsertion hole through the through-hole of the pipe 120.

Even in this case, it is possible to avoid deformation of the mixingblade 48.

According to the above embodiment, an injection molding method forobtaining a molded product by filling molten resin in a product partformed in a mold may include a step of injecting molten resin obtainedby melting resin in an injector 1032 or 30 from the injector 1032 or 30,a step of increasing a temperature of the molten resin flowing in a hotrunner 1020 or 22 to be higher than a melting temperature in theinjector 1032 or 30 by passing through a temperature rising part 1040 or42 provided in a part of the hot runner 1020 or 22, and a step ofleading the molten resin passed through the temperature rising part 1040or 42 to a product part.

Further, according to the above embodiment, an injection moldingapparatus configured to obtain a molded product by filling molten resinin a product part formed in a mold may comprise an injector 1032 or 30which obtains molten resin by melting resin, and injects the moltenresin, a hot runner 1020 or 22 which is a flowing path of the moltenresin, and a temperature rising part 1040 or 42 which is provided in apart of the hot runner 1020 or 22, and increases a temperature of themolten resin to be higher than a melting temperature in the injector1032 or 30.

According to the method and apparatus, a temperature of molten resinflowing in a hot runner is increased to be higher than a meltingtemperature in an injector by passing through a temperature rising part,and a viscosity of the molten resin is lowered at the same time. Thus,it is possible to increase a molten resin flowing distance.

In other words, for example, even when a product part includes a portionforming a thin portion, the molten resin temperature is high, heat of amold is difficult to be removed, and the molten resin easily passesthrough the portion while maintaining a low viscosity, and reaches anend portion of the product part. Thus, it is possible to obtain a moldedproduct free from occurrence of a defect.

Besides, time to keep the molten resin at a high temperature is shorterthan when setting a high resin melting temperature in an injector. Thisprevents weakening of a molded product caused by a change in physicalproperties of molten resin, and occurrence of a defect in externalappearance of a molded product due to generation of gas. In other words,an obtained molded product has a sufficient strength.

Further, to ensure the strength of a molded product, as long ascontrolling a temperature of the temperature rising part and the time tobe held at a high temperature, it is unnecessary to optimize injectionconditions by repeating a test as in the case of using a multipointgate. In addition, as it is unnecessary to use a multipoint gate, apossibility of generating a weld line is eliminated, and the mold costis not increased.

Further, in this case, it is unnecessary to increase the molten resininjection pressure for increasing the molten resin flowing distance.Thus, there is no need to increase the mold clamping pressure foravoiding generation of burrs when the injection pressure is increased.

For the above reasons, it is possible to avoid an increase in the sizeand weight of an injection molding apparatus. Further, a compactdisplacement mechanism is generally inexpensive compared with a largeone, and it is possible to avoid an increase of equipment investment.

The above method may further include a step of stirring the molten resinflowing in the temperature rising part 1040 or 42 by a stirring part1054 or 44. Further, the above apparatus may comprise a stirring part1054 or 44 for stirring the molten resin flowing in the temperaturerising part 1040 or 42.

By the stirring, occurrence of temperature variations in molten resincan be avoided, and consequently, a temperature, consequently aviscosity of molten resin becomes substantially uniform. This avoidsformation of a high viscous portion in molten resin, and it becomes easyto increase a flowing distance of the molten resin.

A stirring part may be provided with the static mixer 1054 or 44.

Stirring by the static mixer requires no power, and for example, anincrease of power consumption for performing injection molding can beavoided. Further, heat transfer and shearing force given to molten resincan be adjusted depending on a shape and structure of a static mixer.Thus, it is possible to control a degree of temperature rise of moltenresin while passing through a static mixer. Further, as a shearing forceto molten resin can be controlled, an injection pressure of an injectorcan be lowered, and a load of the injector can be reduced.

The above method may further include a step of passing the molten resinthat has passed through the temperature rising part 1040, through thecobwebbing prevention part 1042. The above apparatus may furthercomprise a cobwebbing prevention part 1042 provided on the downstreamside of the temperature rising part 1040.

The cobwebbing prevention part prevents transfer of heat of atemperature rising part to the molded product, and can avoid cobwebbingwhile opening a mold.

After the first time injection molding is finished, molten resin mayremain in a temperature rising part. The remained molten resin remainsin the temperature rising part until the next injection molding isperformed, and is kept in an increased temperature state. Thus, there isa possibility that the remained molten resin changes in physicalproperties. If the remained molten resin changed in physical propertiesis led to a product part in the next injection molding, there is apossibility of producing a molded product with an insufficient strengthor unsatisfactory external appearance quality.

To prevent such a possibility, it is considerable to increase a distanceof a flowing path from a temperature rising part to a product part. Theremained molten resin causes a fountain flow when being pushed out bynewly injected molten resin, and adheres to a wall surface of a flowingpath as a skin layer. Thus, if a distance of a flowing path increases,the entire remained molten resin becomes a skin layer. The remainedmolten resin is prevented from being led to a product part. However, inthis case, the size of the injection molding apparatus is increased.

Thus, the above method may further include a step of receiving themolten resin 1000 remained in the temperature rising part 1040 in thelast injection by the slag well 1086 provided on the downstream side ofthe temperature rising part 1040 in the next injection. The aboveapparatus may further comprise the slag well 1086 provided on thedownstream side of the temperature rising part 1040.

With the slag well 1086, the entire remained molten resin can become askin layer in a flowing path from a temperature rising part to a productpart without increasing the flowing path distance. Therefore, the sizeof the injection molding apparatus is not increased.

Further, the above apparatus may further comprise a path opening/closingpart 60 that opens or closes an upstream side flowing path 40 or adownstream side flowing path 50 of a temperature rising part 42.

In this apparatus, for example, when the downstream side flowing path ofthe temperature rising part is closed, by this closing, the molten resinremained in the temperature rising part is isolated from the moltenresin filled in the cavity during injection molding. Therefore, thisinterrupts heat transfer from the molten resin remained in thetemperature rising part or its upstream side to the molten resin filledin the cavity. Thus, the molten resin filled in the cavity isefficiently cooled, and a cycle time to obtain a molded product isreduced.

In the above apparatus, the path opening/closing part may be configuredas a so-called a valve gate. Namely, in this case, the pathopening/closing part comprises a valve member 60 for opening or closingthe upstream side flowing path 40 or the downstream side flowing path50, and a displacement mechanism 54, 90, or 100 for displacing the valvemember.

In the above apparatus, a stirring part 44 may be provided for stirringthe molten resin flowing in the temperature rising part 42. By thestirring, it is possible to avoid occurrence of temperature variationsin molten resin. Therefore, a temperature, consequently a viscosity ofmolten resin becomes substantially uniform. Thereby, formation of a highviscosity portion in molten resin can be avoided, and the molten resinflowing distance can be easily increased.

In the above apparatus, the valve member 60 may be extended in adirection parallel to a longitudinal direction of the stirring part 44,and a passageway 82, which communicates the inlet or outlet of thestirring part 44 with the upstream side flowing path or the downstreamside flowing path, and is inclined to the longitudinal direction of thestirring part, may be provided.

In this structure, the valve member does not interfere the stirringpart.

In the above apparatus, the valve member 60 may be extended in adirection inclined to the longitudinal direction of the stirring part.

Further, in the above apparatus, the stirring part 44 may be providedwith a stirring blade 70, an insertion hole may be formed in thestirring blade 70, and the valve member 60 may be passed through theinsertion hole.

In the above apparatus, the insertion hole may be formed in a portionother than a junction between the stirring blades 70.

The stirring blade is generally formed by joining a plurality of blades.However, when the insertion hole is formed in the junction, the jointstrength is decreased. As long as the insertion hole is formed in aportion other than the joint between the stirring blades 70, even if theinjection pressure is extremely increased, the stirring blade is notdeformed.

In the above apparatus, a center axis of the stirring part 44 may beprovided at a position offset with respect to the central axis of theupstream side flowing path or the downstream side flowing path.

In the above apparatus, the tubular member 120 may be inserted into theinsertion hole, and the valve member 60 may be passed through theinsertion hole through the through-hole of the tubular member 120.

In this structure, deformation of the stirring blade can be avoided.

In the above apparatus, the displacement mechanism 54 may be provided inthe fixed mold 12, and the valve member 60 may open or close thedownstream side flowing path 50.

In this structure, the molten resin in the temperature rising part isisolated from the molten resin in the cavity, the molten resin in thecavity can be efficiently cooled, and a cycle time to obtain a moldedproduct can be easily reduced.

In the above apparatus, the displacement mechanism 90 or 100 may beprovided in the movable mold 14, and the valve member 60 may open orclose the downstream side flowing path 50.

In this structure, a molded product is supported by the valve memberduring mold opening. Therefore, the molded product is prevented fromfalling off.

In the above apparatus, a plurality of temperature rising parts 42 andpath opening/closing parts 60 may be provided.

In this structure, even when the hot runner branches, the effectsdescribed above can be obtained.

The above apparatus may be configured so that the molten resin isindividually supplied from each of the temperature rising parts 42 tothe cavity by individually operating a plurality of path opening/closingparts 60.

In this structure, for example, when there is a wide portion in thecavity, molten resin can be densely filled in the portion by arranging aplurality of path opening/closing parts so that they replenish thefilling amount each other.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   1010: Injection molding apparatus    -   1012: Fixed mold    -   1014: Movable mold    -   1016, 1020: Hot runner    -   1032: Injector    -   1034: Injection nozzle    -   1040: Temperature rising part    -   1042: Cobwebbing prevention part    -   1044: Spool    -   1046: Runner    -   1048: Gate    -   1050: Product part    -   1054: Static mixer    -   1056, 1064: Band heater    -   1058: Mixing blade    -   1062: Tubular member    -   1066: Cobwebbing prevention ring    -   1078: Heat insulating member    -   1086: Slag well    -   1100: Remained molten resin    -   1102: Newly injected molten resin    -   10: Injection molding apparatus    -   12: Fixed mold    -   14: Movable mold    -   16: Runner    -   18: First hot runner    -   22: Second hot runner    -   30: Injector    -   32: Injection nozzle    -   34: Guide path    -   36: Branch path    -   38: Hot nozzle    -   40: Communication path    -   42: Temperature rising part    -   44: Static mixer    -   46: Band heater    -   48: Mixing blade    -   50: Spool    -   52: Nozzle tip    -   54, 100: Hydraulic cylinder    -   56, 102: Piston rod    -   60: Valve shaft    -   70: Stirring blade    -   72: Bypass block    -   82: Passageway    -   90: Motor    -   92: Rotation axis    -   94: Pinion gear    -   96: Rack    -   104: First cam member    -   106: Second cam member    -   108: Convex cam portion    -   110: Concave cam portion    -   120: Pipe

The invention claimed is:
 1. An injection molding apparatus forobtaining a molded product by filling molten resin in a product partformed in a mold, comprising: an injector which obtains molten resin bymelting resin, and injects the molten resin, a hot runner which is aflowing path of the molten resin, a temperature rising part which isprovided in a part of the hot runner, and increases a temperature of themolten resin to be higher than a melting temperature in the injector, apath opening/closing part which opens or closes an upstream side flowingpath or a downstream side flowing path of the temperature rising part,and a stirring part provided with a stirring blade for stirring themolten resin flowing in the temperature rising part, wherein the pathopening/closing part comprises a valve member for opening or closing theupstream side flowing path or the downstream side flowing path, and adisplacement mechanism for displacing the valve member, wherein aninsertion hole is formed in the stirring blade, and the valve member ispassed through the insertion hole, and wherein a tubular member isinserted into the insertion hole, and the valve member is passed throughthe insertion hole through a through-hole of the tubular member.
 2. Theinjection molding apparatus according to claim 1, wherein the stirringpart includes a static mixer.
 3. The injection molding apparatusaccording to claim 1, further comprising a cobwebbing prevention partprovided on a downstream side of the temperature rising part.
 4. Theinjection molding apparatus according to claim 1, further comprising aslag well provided on a downstream side of the temperature rising part.5. The injection molding apparatus according to claim 1, wherein thevalve member is extended in a direction parallel to a longitudinaldirection of the stirring part.
 6. The injection molding apparatusaccording to claim 1, wherein a center axis of the stirring part isprovided at a position offset with respect to a central axis of theupstream side flowing path or the downstream side flowing path.
 7. Theinjection molding apparatus according to claim 1, wherein thedisplacement mechanism is provided in a fixed mold, and the valve memberopens or closes the downstream side flowing path.
 8. The injectionmolding apparatus according to claim 1, wherein two or more thetemperature rising part and path opening/closing part are provided. 9.The injection molding apparatus according to claim 8, wherein the moltenresin is individually supplied from the two or more of the temperaturerising parts to the cavity by individually operating the pathopening/closing parts.